1. Field of the Invention
The present invention relates to a sheet conveying apparatus and an image forming apparatus. The present invention relates to a tabbed sheet regulation unit which is used to convey a tabbed sheet.
2. Description of the Related Art
An image forming apparatus such as a printer and a copying machine has a sheet conveying apparatus which conveys each of plural sheets from a sheet storage portion which stores the sheets. As such sheet conveying apparatus, there is a sheet conveying apparatus of an air sheet feeding system which blows air to the edge of a sheet bundle supported on a tray which can be lifted and lowered, blows up plural sheets, absorbs only one of them to an absorption conveying belt disposed above, and conveys it (see Japanese Patent Application Laid-Open (JP-A) No. 7-196187).
FIG. 13 illustrates an example of such related art sheet conveying apparatus of an air sheet feeding system. As illustrated in FIG. 13, a tray 12 which stacks and supports plural sheets S is provided in a storage case 11 which is a sheet storage portion storing the sheets S so as to be lifted and lowered.
When each of the sheets S is set on the tray 12, the position of the downstream edge in a sheet conveying direction (hereinafter, called the leading edge) of the sheet S is held by a leading edge regulation plate 17 and the position of the upstream edge in a sheet conveying direction (hereinafter, called the trailing edge) of the sheet S is held by a trailing edge regulation plate 13. The positions of both side edges in a direction perpendicular to a sheet conveying direction (hereinafter, called a width direction) are held by side regulation plates 14.
The storage case 11 has in its upper portion an absorption conveying portion 20 which absorbs and conveys the sheet S, and an air blowing portion 30 which blows air to the edge of the sheet bundle on the tray, blows up the plural sheets S, and separates each of them.
The absorption conveying portion 20 has an absorption conveying belt 21 which is entrained onto a belt drive roller 41 and absorbs the sheet S to convey it in a right direction in the drawing, and an absorption fan 36 which causes a negative pressure for absorbing the sheet S to the absorption conveying belt 21. The absorption conveying portion 20 has a suction duct 22 which is arranged inside the absorption conveying belt 21 and takes in air through a suction hole formed in the absorption conveying belt 21. To turn on and off the absorption operation of the absorption fan 36, the absorption conveying portion 20 has an absorption shutter 37 between the absorption fan 36 and the suction duct 22.
The air blowing portion 30 has a loosening nozzle 33 and a separation nozzle 34 which blow air to the upper portion of the stored sheet bundle, a separation fan 31, and a separation duct 32 which sends air from the separation fan 31 to the nozzles 33 and 34.
Part of air taken in the direction of the arrow C by the separation fan 31 passes through the separation duct 32, is blown in the direction of the arrow D by the loosening nozzle 33, and blows up several upper sheets of the sheet bundle supported on the tray 12. Other air is blown in the direction of the arrow E by the separation nozzle 34 and separates the uppermost one of the several sheets blown up by the loosening nozzle 33 to press the sheet to the absorption conveying belt 21.
Such sheet conveying apparatus is often adopted in a high-speed apparatus which can convey over 70 A4-size sheets per minute. The tray 12 has a mechanism which is lifted and lowered in a vertical direction by the driving unit, not illustrated, while maintaining the substantially horizontal state.
FIG. 14 is a plan view illustrating the detail of the storage case 11. The trailing edge regulation plate 13 which regulates the trailing edge of the sheet can be moved in parallel with a sheet conveying direction indicated by the arrow H. The side regulation plates 14 and 16 which regulate the side edges of the sheet can be moved in a sheet width direction indicated by the arrow V.
In this manner, the trailing edge regulation plate 13 and the side regulation plates 14 and 16 can be moved. Therefore a smallest size sheet SS and a largest size sheet LS can be stacked and supported on the tray 12. The trailing edge regulation plate 13 is provided so as to be moved only in the center portion in a width direction of the tray 12 so as not to interrupt the movement of the side regulation plates 14 and 16.
A trailing edge separation portion 18 which regulates the position of the trailing edge which is the upstream edge in a sheet conveying direction of an uppermost sheet Sa is provided on the trailing edge regulation plate 13 so as to be moved in up and down directions. The trailing edge separation portion 18 has a protrusion portion 18D which protrudes from a regulation portion surface 13C of the trailing edge regulation plate 13 illustrated in FIG. 13 and presses the trailing edge of the uppermost sheet Sa from above. As illustrated in FIG. 13, a separation aid sheet 18E made of a material having a high friction coefficient for adding resistance to the upper surface of the stacked sheet is stuck onto the lower surface of the protrusion portion 18D, that is, the sheet abutment surface.
When the uppermost sheet Sa is conveyed by a protrusion length S1 of the protrusion portion 18D illustrated in FIG. 13, the trailing edge separation portion 18 is lowered so as to be abutted on a sheet Sb immediately below the uppermost sheet Sa. The conveyance of the sheet Sb immediately below the uppermost sheet Sa following the uppermost sheet Sa being conveyed can be prevented by a friction force caused by the weight of the trailing edge separation portion 18 thereby preventing the occurrence of the overlap conveyance. The protrusion portion 18D is abutted on the surface of the tray 12 when there are no set sheets.
In FIG. 13, a supporting portion 18A is provided in the trailing edge separation portion 18 and engages an engaging portion 13E provided in the trailing edge regulation plate 13. A ball bearing or a roller with a surface having a low friction resistance is provided in the supporting portion 18A, so that the movement of the trailing edge separation portion 18 in the direction of the arrow G in the drawing can be smooth.
In recent years, the image forming apparatus has been often required to make a booklet. A sheet having a tabbed edge (hereinafter, called a tabbed sheet) as a partitioning sheet can be used. With this, the tabbed sheet need be conveyed from the sheet conveying apparatus. Therefore such sheet conveying apparatus of an air sheet feeding system need to convey the tabbed sheet.
FIG. 15A is a diagram illustrating the state that a tabbed sheet TS of a predetermined size is set in the sheet conveying apparatus of an air sheet feeding system. The tabbed sheet TS is supported on the tray 12 in the state that a tab portion TSa is located upstream in a sheet conveying direction. The side regulation plates 14 are abutted on both side edges of the tabbed sheet TS. The trailing edge regulation plate 13 is abutted on the tab portion TSa of the tabbed sheet TS.
The conveying operation is started in such state. As illustrated in FIG. 15B, air is blown from the loosening nozzle 33 and the separation nozzle 34 to the leading edge of the tabbed sheet TS. The trailing edge regulation plate 13 is provided only in the center portion. Some tabbed sheets TS in which the tab portions TSa are not abutted on the trailing edge regulation plate 13, e.g., the uppermost and second uppermost tabbed sheets TS, are moved rearward by a width TD of the tab portion TSa at the maximum in the direction of the arrow T.
When the tabbed sheet TS in which the tab cannot be regulated by the trailing edge regulation plate 13 is moved rearward, the wind pressure is weakened as the tabbed sheet TS is far away from the loosening nozzle 33. Therefore, as illustrated in FIG. 16, a leading portion TF of the uppermost tabbed sheet TS1 and the second uppermost tabbed sheet TS2 in which the tabs cannot be regulated by the trailing edge regulation plate 13 cannot be sufficiently blown up and is hung down. Air blown from the loosening nozzle 33 is hard to enter into between the sheets, and the leading edge of the sheet cannot be appropriately loosened.
Alternatively, the blowing-up of the sheet is not stable and other sheets are affected so as to be in the unstable blowing-up state. The sheets are repeatedly moved up and down in the direction of the arrow R illustrated in FIG. 16. In such blowing-up state, the disadvantage such as a jam due to overlap conveyance and absorption failure to the absorption conveying belt 21 and sheet corner folding is caused.
The conveyance of the tabbed sheet is also required, not only in the sheet conveying apparatus of an air sheet feeding system, but also in the sheet conveying apparatus which is of a sheet conveying system by a roller and lifts and lowers the tray stacking the sheet by a lifter mechanism.
In the sheet conveying apparatus which conveys the sheet by the roller, as in the sheet conveying apparatus of an air sheet feeding system, the tab cannot be regulated by the trailing edge regulation member and the tabbed sheet may be shifted rearward. When the roller conveying the sheet is arranged at the leading edge of the sheet, the tabbed sheet cannot be conveyed, resulting in the conveying failure of the sheet. When the sheet can be conveyed, the timing to convey the sheet is largely shifted. Therefore, the sheet interval may be increased to lower the productivity and a delay jam may be detected.
To address such disadvantage, it is considered that a tab guide only for the tabbed sheet which is abutted on all the tab portions TSa of the tabbed sheets TS is attached as an option (see JP-A No. 2000-229732 and U.S. Pat. No. 7,290,764).
FIG. 17 is a diagram illustrating the state that a tab guide 13M is provided on the upper surface of the tray 12. The tab guide 13M is provided on the upper surface of the tray 12 so that the trailing edge position of the tabbed sheet TS can be regulated, and the tabbed sheet TS can be reliably conveyed.
In such related art sheet conveying apparatus and the image forming apparatus having the same, the tab guide should be attached to the upper surface of the tray. This is because when the tab guide 13M illustrated in FIG. 17 is provided, the region indicated by the slant lines of the tab guide 13M is overlapped with the tray 12 and thereby the tab guide 13M cannot be fixed to the storage case 11. The tab guide abutted on all the tab portions TSa of the tabbed sheets TS should be attached to the upper surface of the tray 12.
As illustrated in FIG. 18, the tabbed sheet TS is conveyed. As the remaining amount of the tabbed sheets TS is decreased, the tray 12 is lifted and the tab guide 13M is lifted together with the tray 12. In order that the lifted tab guide 13M cannot collide with a component 40 configuring the image forming apparatus body, the tab guide 13M need be low.
As illustrated in FIG. 19, the tab guide 13M is set to be low, the height which can guide the tabbed sheet TS is decreased accordingly. The amount of the tabbed sheets TS stacked is greatly reduced. As a result, the number of feedings of the tabbed sheet TS is increased, and the operability and productivity of the apparatus are very low.
The present invention provides a sheet conveying apparatus and an image forming apparatus which can obtain high operability and productivity when a tabbed sheet is conveyed.